Pediatric cancers represent an understudied area in oncology. The great majority of cancer research is dedicated to understanding adult malignancies, such as cancers of the breast, colon, lung and skin. However, pediatric cancers most commonly arise in distinct tissues, such as brain, bone, and blood. The biological landscape of such developing tissues is believed to confer a distinct susceptibility to oncogenic insults, but our understanding of the molecular basis of this phenomenon is still in its infancy. This application focuses on a novel agent implicated in the etiology of several bone and soft tissue tumors (BSTTs), a class of tumors that preferentially targets children and adolescents. TRE17 translocation occurs in two distinct BSTTs, aneurysmal bone cyst (ABC) and nodular fasciitis (NF), leading to its high level expression. Our screening of a wide panel of primary human tumors further revealed high expression specifically in a high percentage of alveolar rhabdomyosarcoma (ARMS) cases. Rhabdomyosarcoma is the most common pediatric soft tissue sarcoma; of the various subtypes, ARMS carries the worst prognosis. My research is aimed at elucidating the pathogenic mechanisms of TRE17. Our recent work focusing on its functions in the context of ABC revealed that it functions cell-autonomously to promote tumor cell proliferation/survival, but also regulates the tumor microenvironment by inducing the production of multiple cytokines, chemokines, and growth factors, in a manner strictly dependent on its USP activity. We further identified NF?B and STAT3 as key effectors of TRE17 in ABC pathogenesis. Both of these transcription factors are widely dysregulated in cancer, often coordinately, where they function pleiotropically to promote multiple aspects of tumor growth and metastasis. We hypothesize that TRE17 plays a key role in ARMS pathogenesis, and that NFB and STAT3 function as critical effectors. This proposal will determine the requirement of these three factors both in vitro and in vivo. In vitro analyses will assess their rle in cell proliferation, survival, and cytokine/growth factor production, and will include examining their role within the cancer cell stem (CSC) subpopulation, which has been reported to be dependent on NF?B and STAT3 in other cancers. In vivo studies will examine their role in tumor formation, tumor maintenance, and metastasis. If successful, these studies would provide three novel targets for therapeutic intervention in ARMS. Notably, inhibitors for NF?B and STAT3 pathways are already being avidly developed for other cancers and immune disorders. Furthermore, TRE17-specific USP inhibitors might function as effective therapeutic agents for not only ARMS, but also other BSTTs driven by TRE17 overexpression. USP inhibitors are particularly appealing since TRE17 exhibits such limited expression, minimizing the likelihood of side effects.